No, I don't believe the console command works for reducing militancy. To get around this I ended up scripting an event in. I've added the event below, but note this resets militancy back to zero. If you want a different level then you will have to adjust accordingly.

Note that the effects won't show until the next round of tax hits on the population, and if a region is already in serious unrest the levels of unrest (i.e. strikes, etc.) will only gradually reduce in intensity. Also, the levels of contentment and militancy will automatically begin changing again according to the situation in your game, so even though militancy may reduce to zero in one province it will begin climbing again as normal.

Looking through the event files within the game structure gives a good idea as to what can be edited and added through events. The best place to add in a new event is the "Plugin_...." files under the events folder. In any case, wherever a new event is filed just ensure that event file is included as one listed in the appropriate campaign script file in the events folder, named for example 1850 GC, 1870 FPW, etc.

Can I use the console to make it work? Also, will it work for other countries than Romania - like playing as one country and fire it and then as another and fire it too, will it work for both or fire two events for romania?

Yes, the event will work for any country. You will just need to change the faction tag to whichever one you want, and changing the event date means it can be used anytime you wish. The only thing that seems to prevent multiple events firing is using the same event name, so adding a number or renaming each occurrence solves that issue and allows the event to fire as many times as wanted. There are other ways of adding in text that make the same event fire regularly but that's a bit more complex.

I've tried the console command and it has never worked. Unless someone else has successfully done it, then I don't know any other way to do it.